1. Field of the Invention
The field of the invention relates to metering pumps for pumping relatively precise volumes of fluid.
2. Brief Description of the Prior Art
Valveless, positive displacement metering pumps have been successfully employed in many applications where safe and accurate handling of fluids is required. The valveless pumping function is accomplished by the synchronous rotation and reciprocation of a piston in a precisely mated cylinder bore. One pressure and one suction stroke are completed per cycle. A duct (flat portion) on the piston connects a pair of cylinder ports alternately with the pumping chamber, i.e. one port on the pressure portion of the pumping cycle and the other on the suction cycle. The mechanically precise, free of random closure variation valving is performed by the piston duct motion. A pump head module containing the piston and cylinder is mounted in a manner that permits it to be swiveled angularly with respect to the rotating drive member. The degree of angle controls stroke length and in turn flow rate. The direction of the angle controls flow direction. This type of pump has been found to perform accurate transfers of both gaseous and liquid fluids.
In some applications, it is necessary to provide two or more discharges of a fluid in selected proportions. This has typically been accomplished by using two separate pumps, or one pump and a multi-position flow diverter such as a solenoid valve.
A valveless positive displacement pump including multiple ports is disclosed in U.S. Pat. No. 4,008,003. The pump includes a cylinder divided into a pair of working chambers, each of the chambers communicating with two ports. In essence, the disclosed pump operates as two separate pumps.